This invention relates generally to operator-energized drive systems and is particularly directed to a drive system for converting operator-initiated forces to the rotational displacement of a drive wheel.
Operator-energized wheel drive mechanisms generally comprise a large rotatable sprocket and a pair of pedals secured thereto with a flexible, endless chain connecting the pedal carrying sprocket to a drive sprocket mounted to a drive wheel such as in a velocipede. Such arrangements are typically found in a conventional bicycle and in stationary exercise apparatus. Rotational displacement of the pedals by the operator causes the operator's feet engaging the pedals to follow a circular path with the pedals oppositely disposed such that at one point during each revolution the pedals are positioned vertically relative to one another. The pedals must then be moved from this vertical "dead center" position to permit force imparted to the pedals to be delivered as rotary motion to the drive wheel of the apparatus.
This rotating crank arrangement is inefficient since maximum leverage is applied by the operator only during a portion of each stroke, with the leverage at the top and the bottom of the circle of rotation being very small. Thus, over a large portion of the drive pedal displacement range a minimal drive force is applied by the operator even though energy must be expended for continued rotational displacement of the drive sprocket in order to position it in an orientation where an increased drive force may be applied thereto.
In an attempt to improve the efficiency of such a pedal operated drive mechanism, various reciprocating pedal arrangements have been proposed. This approach has generally included paths of displacement of the pedals which more closely approximate straight line movement adapted for the application of the strongest and most extended leg thrust of the operator. Thus, the pedals are reciprocally displaced along generally vertical axes by means of an essentially tangential force applied by the operator. In the past such reciprocating pedal drive mechanisms designed to provide a nearly constant leverage have been overly complex and expensive and frequently have required gears in order to reduce the energy required for operation over extended periods of time. Because of these shortcomings, reciprocating pedal drive systems have not enjoyed general acceptance and widespread usage.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing an operator powered reciprocating drive system capable of operating in either of two modes. In a first mode, the pedals are displaced in an alternating, reciprocating manner along a generally vertical axis. In a second mode of operation the pedals are displaced together along a generally vertical axis in a reciprocating manner in combination with the alternate, reciprocal, vertical displacement of a seat upon which the operator is positioned. The present invention thus makes more efficient use of the operator's strength and weight in imparting rotation to a drive wheel.